could very well end democracy.
I'd argue that the forces that created the possibility of a Trump/Sanders presidency are more dangerous than those candidates individually. As such, a vote for Hillary is probably worse in the long term. At least Trump would be such a disaster that it would force change. Trump might not be back next time, but someone adept at harnessing pent-up frustration and anger sure will be.
You're assuming that there would BE a next time if Trump became President. I'm not certain that is a valid assumption
Given his reaction to criticism during this campaign, what would he do if China, Russia, or North Korea insulted him? I think there would be a very real possibility that Trump would order some action (either a deliberate diplomatic insult or an accidental faux pas or some good old fashioned saber rattling) in defense of his bruised ego that would escalate the situation to the point where a war of words would transition to a war of bullets or an economic battle. And if his Secretary of State tried to calm things down, I wouldn't be surprised if he told him or her "You're fired!"
When Trump is the 500 pound gorilla in the room, he's fully willing and able to throw his weight around. But when you put two or more gorillas in a room, if they become antagonistic towards one another it's probably not going to end well for one or all of the gorillas.